Fatty acid transport and incorporation into human erythrocytes in vitro.

When human erythrocytes were incubated in vitro with (14)C-labeled free fatty acids bound to serum albumin, labeled fatty acids were incorporated into erythrocyte triglycerides and phospholipids. The first step in this reaction was the transfer of free fatty acids from the albumin to the cells. This transfer was rapid and reversible. The acids were distributed between albumin and cells according to the relative quantities of albumin and cells present. Each acid had a different distribution coefficient. At equilibrium, relatively larger fractions of the stearic and palmitic acids and smaller fractions of the oleic and linoleic were associated with the cells. All these fatty acids were then slowly incorporated into phospholipids and triglycerides. The rate of incorporation of each was a function of its concentration in the cells, but larger fractions of the oleic and linoleic were incorporated than of the stearic, palmitic, myristic, or lauric. The two processes of transfer and incorporation thus had almost opposite selectivities for the different fatty acids. As a result, the fatty acids incorporated into triglycerides and phospholipids resembled in composition the fatty acids on the albumin except for moderately less stearic acid.